Electroless copper plating bath



United States Patent 3,415,666 ELECTROLESS COPPER PLATING BATH SatoshiNagai, Tokyo, Koji Furumoto, Yokohama, Hisae Moriya, Urawa-shi, andSakae Akimoto, Kawasaki-ski, Japan, assignors to Asahi Dow Limited,Tokyo, Japan, a corporation of Japan No Drawing. Filed June 16, 1966,Ser. No. 557,893 Claims priority, application Japan, June 19, 1965,

0/36,245 2 Claims. (Cl. 106--1) The present invention relates to anelectroless copper plating bath. Heretofore, an electroless platingprocess has been used in order to impart electroconductivity to asurface of an insulating material, e.g. a material made of wood, paperor plastics. Electroless copper plating is to use copper mirrorreaction. The electroless copper plating is practiced by dipping anelectrically insulated material in a plating bath to reduce and depositcopper on the surface of the material. The plating bath is made byadding a reductive aqueous solution containing alkalis to an aqueoussolution of Formalin, hydrazine, hydroxylamines, hydroquinone of acidmetal salts such as sodium hypophosphite. The Forma-lin is most familiaras the base of the plating bath because it is the cheapest. However, the

Formalin base plating bath has fault that reduction of Formalinproceeds, once prepared and even before and after plating, to depositcopper in the bath and copper ion substantially disappears only after 2or 3 hours, with the result that the plating bath does not work at all.Hereinafter, the time required from which copper begins to deposit inthe electroless plating bath is referred to as holding time.

From a practical point of view, as above-mentioned the holding time isso short that a great trouble is caused in the operation, and that thecharacteristic of copper film produced is not so good.

An object of the invention is to provide an improved plating bath.Another object of the present invention is to provide an electrolesscopper plating bath of good stability and having extended holding time.The other object is to provide an electroless copper plating bath whichcan deposit a copper film enabling to electroplate a pretreated body tobe plated in a short time (1-2 minutes). Further object is to provide anelectroless copper plating bath in which a compact and lustrouselectroless copper film is deposited on a body to be plated.

According to the present invention, an aqueous solution of acid salt ofcopper mentioned above and a reducing aqueous solution are mixed orsmall amounts of sodium thiosulfate and lower alcohol are added to thereducing aqueous solution, thereby effectively depositing copper on thepretreated body to be plated in a short period of time. The depositionof copper, however, ceases in the bath for a prolonged period of timewhen the plating of body to be plated is not carried out therewith.Accordingly, the holding time of the bath is remark-ably extended beforeplating, thereby providing a good working efiiciency and depositing onthe body to be plated the copper film having excellent characteristicfeatures. Thus, the present invention is advantageous from theindustrial point of view.

Thus, the present invention is to provide an electroless copper platingbath prepared by adding 0.000001- 0.100000 part by weight of sodiumthiosulfate and 0.00080-2.400000 parts by weight of lower alcohol to 100parts by weight of an electroless copper plating solution consisting of35-70 parts by weight of copper sulfate, 20-200 parts by weight ofFormalin, 17-340 parts by weight of Rochelle salt, 5-100 parts by weightof sodium hydroxide, 8-160 parts by weight of sodium carbonate and 1,000parts by volume of water. It is, however, preferable to add sodiumthiosulfate and lower alcohol to 3,415,666 Patented Dec. 10, 1968 add toa mixture when prepared by mixing an aqueous solution of acid metal saltcontaining copper sulfate and Formalin and a reducing aqueous solutioncontaining sodium hydroxide, Rochelle salt and sodium carbonate, arepreviously added to the reducing aqueous solution.

Suitable lower alcohol to be used in the present invention includes suchas methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol,butyl alcohol, isobutyl alcohol and the like. In the electroless copperplating bath according to the present invention, when the amount ofsodium thiosulfate added thereto is less than 0.00001 part by weightbased on 100 parts by weight. of an electroless copper plating solution,the velocity of reaction of the electroless copper plating solutionbecomes so fast and the holding time of said bath is so shortened thatan effeet and advantage cannot be obtained as desired similarly to theconventional electroless copper plating bath. Furthermore, when morethan 0.100000 part by Weight of sodium thiosulfate is added thereto, thedeposition of copper does not take place at all on the surface of bodyto be plated and the function as the electroless copper platin solutionis lost.

Furthermore, in the electroless copper plating bath of this invention,when the amount of lower alcohol added thereto is less than 0.000080part by Weight the copper deposited on the surface of body to be platedhas no luster at all and when it is more than 2.400000 parts by weight,sodium thiosulfate does not completely dissolve, and c0nsequently theholding time of the electroless copper plating solution cannot beextended. The holding time of the electroless copper plating bathaccording to this invention has more than about forty times that of theconventional electroless copper plating solution. Accordingly, in aprocess for the industrial scale operation the conventional bath typemethod can be altered to an automatic continuous method, therebyaccomplishing a drastic curtailment of production cost. When theelectroless copper plating bath is used, furthermore, the film of copperdeposited on the surface of body to be plated had good luster andsubsequent process such as electro plating of copper, nickel, chrome orthe like can be smoothly carried out with ease, thereby obtaining goodluster on a deposited metal. Still more, one of the great advantages ofthe process of this invention is that bufling which is extremelyhazardous for a body having low thermal resistance is not required atall.

The present invention will be further explained fully by referring tothe following examples.

EXAMPLE 1 First, an aqueous solution of acid metal salt and a reducingaqueous solution were prepared respectively according to theformulations set forth hereinbelow.

A. Aqueous solution of acid metal salt:

Copper sulfate g 18 Formalin g 100 Water cc 500 B. Reducing aqueoussolution:

Rochelle salt g Sodium hydroxide g 25 Sodium carbonate g 40 Water cc 500Next, the electroless copper plating bath was prepared by mixing theabove-mentioned two solutions with each other and adding as additives0.019 g. of sodium thiosulfate and 3.2 g. of ethyl alcohol thereto withmixing.

3 EXAMPLE 2 By the same manner as in Example 1, an electroless copperplating bath was prepared according to the following formulations.

A. Aqueous solution of acid metal salt:

An electroless copper plating bath was prepared according to thefollowing formulations by the same manner as in Example 1.

A. Aqueous solution of acid metal salt:

Copper sulfate g- 5 Formalin g 29 Water cc 500 B. Reducing aqueoussolution:

Rochelle salt g 25 Sodium hydroxide g 6 Sodium carbonate g- 11 Water cc500 C. Additive:

Sodium thiosulfate g 0.0048

Butyl alcohol Mg 2.4

Comparative Example 1 For comparison, an electroless copper platingsolution was prepared by an aqueous solution of acid metal salt and areducing aqueous solution previously prepared respectively by thefollowing formulations.

A. Aqueous solution of acid metal salt:

Copper sulfate g 18 Formalin g 100 Water cc 500 B. Reducing aqueoussolution:

Rochelle salt g 85 Sodium hydroxide g 25 Sodium carbonate g 40 Water cc500 The electroless copper plating baths and the electroless coppersolution illustrated respectively in the above-mentioned Examples 1-3and Comparative Example 1 were allowed to stand, as they are. Theholding times thereof were measured with the result as denoted in thefollowing table. The holding time was determined by the visualobservation at the moment when the foam of hydrogen gas just begins togenerate.

TABLE Example No: Holding time (hr.) 1 80 3 100 Comparative Example 1 2As is clear from the above results, the holding time of the electrolesscopper plating bath distinctively extends over for a long space of time,compared with that of the conventional electroless copper platingsolution.

Next, the samples of ABS resin (acrylonitrile-butadienestyrenecopolymer) subjected to pretreatment, i.e. (1) surface roughing, (2)degrease-washing with water, (3) surface cleaning, (4) washing withwater, (5) sensitization, (6) washing with water, (7) activation and (8)washing with water, were respectively immersed in the electroless copperplating baths of Examples 1-3 and the electroless copper platingsolution of Comparative Example 1, so that the time required fordepositing a copper film of 0.3g in thickness capable of enablingsubsequent electro plating, can be measured. As a result, in each caseof Examples 1-3 it took one minute 30 seconds and in case of ComparativeExample 1, 12 minutes. Furthermore, the luster of copper film attainedin Examples 1-3 using the electroless copper plating bath of thisinvention was precise and good, compared with that attained inComparative Example 1 using the conventional electroless copper platingsolution.

EXAMPLE 4 An electroless copper plating bath Was prepared according tothe following formulations.

A. Aqueous solution of acid metal salt:

Copper sulfate g 17.5

Formalin g Water cc 500 B. Reducing aqueous solution:

Rochelle salt g 42 Sodium hydroxide g 22.5

Sodium carbonate g 10 Water cc 500 C. Additive:

Sodium thiosulfate g 0.005

Propyl alcohol g 3 The resultant electroless copper plating bath wasallowed to stand for measuring its holding time. As a result, theholding time was hours. Furthermore, the sample of ABS resin pretreatedby the same manner as in the aforementioned example was immersed in saidbath to measure the depositing time for obtaining a copper film of 0.3;in thickness. As a result, it was 1 minute 30 seconds.

EXAMPLE 5 An electroless copper plating bath was prepared according tothe following formulations in the same manner as in Example 1.

A. Aqueous solution of acid metal salt:

Copper sulfate g 15 Formalin g 100 Water cc 500 B. Reducing aqueoussolution:

Rochelle salt 42 Sodium hydroxide g 22.5

Sodium carbonate g 10 Water cc 500 C. Additive:

Sodium thiosulfate g 0.001

Isopropyl alcohol g 1 The resultant electroless copper plating bath wasal lowed to stand for measuring its holding time. As a result, it was 90hours. Furthermore, the sample of ABS resin pretreated by the samemanner as in the aforementioned example was immersed in said bath tomeasure the depositing time for obtaining a copper film of 0.3;1. inthickness. As a result, it was 1 minute 30 seconds.

As above, besides that the holding time of the electroless plating bathof the present invention extends over a long space of time, as comparedwith the conventional electroless solution, its velocity of thedeposition of copper on a body to be plated is fast, its copper film hasa precise luster and its working efficiency is improved. Thus, thepresent invention is to make a distinctive contribution to theindustries concerned.

5 6 What is claimed is: propyl alcohol, isopropyl alcohol, butyl alcoholand iso- 1. An electroless copper plating bath comprising butyl alcohol.0.000001-100000 part by weight of sodium thiosulfate, References Cited100 parts by welght of an electroless copper platlng solu- 5 tionconsisting of 35-70 parts by weight of copper sulfate, 3,307,972 3/1967Ehrhardt 1061 XR 20-200 parts by weight of Formalin, 17-340 parts by3,370,974 2/1968 Hepfer 7 XR Weight of Rochelle salt, 5-100 parts byweight of sodium hydroxide, 8-160 parts by weight of sodium carbonateJULIUS FROMEPr'mary Exammer' and 1000 parts by volume of water. 10 L.HAYES, Assistant Examiner.

2. An electroless copper plating bath of claim 1, U S C1 XR whereinlower alcohol is one kind or more selected from the group consisting ofmethyl alcohol, ethyl alcohol, 160

1. AN ELECTROLESS COPPER PLATING BATH COMPRISING 0.000001-100000 PART BYWEIGHT OF SODIUM THIOSULFATE, 0.0000080-2.400000 PARTS BY WEIGHT OFLOWER ALCOHOL, IN 100 PARTS BY WEIGHT OF AN ELECTROLESS COPPER PLATINGSOLUTION CONSISTING OF 3.5-70 PARTS BY WEIGHT OF COPPER SULFATE, 20-200PARTS BY WEIGHT OF FORMALIN, 17-340 PARTS BY WEIGHT OF ROCHELLE SALT,5-100 PARTS BY WEIGHT OF SODIUM HYDROXIDE, 8-160 PARTS BY WEIGHT OFSODIUM CARBONATE AND 1000 PARTS BY VOLUME OF WATER.